1. Field of the Invention
This invention relates to head-tail discrimination of electronic chip components such as chip resistors, chip capacitors, chip diodes, chip transistors and chip IC's. More particularly, the invention concerns a method and apparatus for performing head-tail discrimination of chip components prior to mounting them onto circuit boards for example.
2. Description of the Prior Art
In automatic mounting of chip components to circuit boards, it is known to use a vibratory parts feeder which has a helical transfer path extending from a central portion of a circular feeder body to a peripheral portion thereof. The chip components are placed in a hopper portion provided at the central portion of the feeder body, and successively transferred along the helical path by imparting vibration to the feeder body. The chip component, after having been transferred to the peripheral portion of the feeder body, is picked up by a robotic chip mounter for mounting to a corresponding circuit board.
In such a parts feeder, the chip components are randomly placed in the hopper portion, so that many of the chip components are inevitably transferred with their head sides down. Thus, it is necessary to make head-tail discrimination of the chip components during transfer thereof, and to reject the improperly oriented chip components before feeding to the chip mounter. The rejected chip components are acted by a pawl for example, and returned to the hopper portion of the feeder body for re-feeding.
One way to perform head-tail discrimination of chip components is to arrange a photosensor above the helical path of the parts feeder. The photosensor detects the light beams reflected by the surface of each chip component to produce a detection signal which is processed to determine head or tail of the chip component by utilizing difference in light reflectivity between the head and tail sides of the component.
However, this manner of head-tail discrimination is disadvantageous in various respects. First, the photosensor is capable of making head-tail discrimination only chip-by-chip, so that efficiency of head-tail discrimination is very low. Second, the single photosensor (only one bit or picture element) fails to provide reliable head-tail discrimination. Further, the vibratory parts feeder is not capable of transferring the chip components at a constant speed, so that the head-tail discrimination conducted at the vibratory parts feeder inherently has the likelihood of being unreliable regardless of the type of sensors used for head-tail discrimination.
It is conceivable to increase the reliability of head-tail discrimination by arranging a plurality of photosensors above the helical path of the vibratory parts feeder. However, satisfactory efficiency and reliability cannot be obtained as long as head-tail discrimination is conducted at the vibratory parts feeder.